Heavy-duty diesel engines which are used largely in commercial vehicles are subject to increasing regulation of emission levels. It is therefore important to provide such engines with measures to reduce harmful emissions, especially particulates, and nitrogen oxides (NOx). Selective catalytic reduction (SCR) is a technology which has been introduced to reduce emissions of NOx by reducing the NOx to nitrogen. Ammonia-SCR systems react ammonia (NH3) with the NOx to form nitrogen (N2) and water (H2O). There are three reaction pathways:4NH3+4NO+O2→4N2+6H2O2NH3+NO+NO2→2N2+3H2O8NH3+6NO2→7N2+12H2O
Any source of ammonia can be used but most commonly the source is an aqueous solution of urea. This decomposes in the exhaust stream in two stages to form ammonia and carbon dioxide (CO2). The commercial standard form of urea sold for this purpose in Europe is a 32.5% aqueous urea solution, known as AdBlue™ which conforms to DIN 70070 standard for urea solution for use in SCR systems.
A concern with the introduction of such an additive is the control and monitoring of the use of suitable quality product which conforms to the accepted regulatory standard. With the introduction of mandatory emission control measures in many countries, the use of SCR technology will become regulated and therefore liable to inspection. Dilution of conforming Adblue or the use of Adblue from a non-conforming source should be capable of being monitored by the transport authorities' inspectors in order to ensure that vehicle emissions of NOx using SCR technology are suitably controlled. It is an object of the present invention to provide a tagging system for urea solutions for use in SCR systems and to provide a method of tagging urea and determining the source of a urea solution.